Compensated multi-function hydraulic system

ABSTRACT

A hydraulic system capable of adjusting the output of a variable delivery pump in response to the varying demands of any one of at least two hydraulically operated functions, the system comprising at least two control valve means each capable of performing a separate function. Each of the valve means is connected to its own separate compensator valve means, the said compensator valve means being connected in series one with the other and being capable of delivering the necessary amount of hydraulic fluid to its respective control means in accordance with the full needs thereof and diverting the remainder of the fluid to the next following compensator valve means. The system also includes means connected to the compensator valve means farthest from said pump for sensing the total requirement of the system and for adjusting the output of the pump in response thereto. In preferred embodiments, the means for sensing and adjusting include a restricted orifice means, a valve means, and means for sensing the pressure across the orifice means, the valve means being connected through one of its ports to an adjustor means for adjusting the output of the pump, and being normally biased by the means for sensing the pressure drop so as to actuate said adjustor means in favor of providing a minimal continuous flow through said system regardless of the total requirements of the system.

United States Patent Sievenpiper [451 Apr. 22, 1975 1 COMPENSATEDMULTl-FUNCTION HYDRAULIC SYSTEM Donald A. Sievenpiper, Kalamazoo, Mich.

[73] Assignee: General Signal Corporation,

Rochester, NY.

[22] Filed: Aug. 30, 1973 [21] Appl. No.: 392.901

[75] Inventor:

Primary E.\'aminer-Edgar W. Geoghegan Attorney, Agent, or FirmP0llock,Philpitt & Vande Sande [57] ABSTRACT A hydraulic system capable ofadjusting the output of a variable delivery pump in response to thevarying demands of any one of at least two hydraulically operatedfunctions, the system comprising at least two control valve means eachcapable of performing a separate function. Each of the valve means isconnected to its own separate compensator valve means, the saidcompensator valve means being connected in series one with the other andbeing capable of delivering the necessary amount of hydraulic fluid toits respective control means in accordance with the full needs thereofand diverting the remainder of the fluid to the next followingcompensator valve means. The system also includes means connected to thecompensator valve means farthest from said pump for sensing the totalrequirement of the system and for adjusting the output of the pump inresponse thereto. In preferred embodiments, the means for sensing andadjusting include a restricted orifice means, a valve means, and meansfor sensing the pressure across the orifice means, the valve means beingconnected through one of its ports to an adjustor means for adjustingthe output of the pump, and being normally biased by the means forsensing the pressure drop so as to actuate said adjustor means in favorof providing a minimal continuous flow through said system regardless ofthe total requirements of the system.

10 Claims, 1 Drawing Figure COMPENSATED MULTl-FUNCTION HYDRAULIC SYSTEMBACKGROUND OF THE INVENTION This invention relates to compensatedmulti-function hydraulic systems. More particularly. this inventionrelates to a unique system for adjusting the output of a variabledelivery pump in response to the varying needs of any one of a pluralityof hydraulically operated control valves. without regard to whichcontrol valve varies in its demands.

With the advent of an increased need for heavy mechanical technology hascome an increased demand for heavier and more complex hydraulic systems.With this increased demand has come a significant demand for hydraulicsystems capable of performing a plurality of functions either insequence or simultaneously one with the other. Seeking to meet thisneed. there has arisen an active interest in the development ofahydraulic system capable of performing a multitude of functionsefficiently. and without undue power losses (e.g.. undue heat losses).

An excellent example of the need for such a system is displayed on acrawler-mounted excavator. In this circuit it is often desirable. and inmany instances necessary. to operate the main boom. the stick arm. andthe bucket simultaneously. All this must be accomplished duringconditions when loads at many or all points within the system vary dueto dynamic inputs from another function. This. of course. requiresextremely close control of flow and pressure.

Several attempts have been made to effect such controls. For example.one known technique employs the use of several pumps. each supplying aportion of the circuit. Such a circuit usually requires means whichcombine the pump flows under certain conditions when high speed of onefunction is required. There are several drawbacks to such a system, themost obvious one being the need to employ several pumps with combinedflow means and the expense and complexity connected therewith.

Another known technique for achieving control of a system when it isperforming a multitude of functions is to use what are known aspressure-compensated valve components" in the system. These valvecomponents. generally of the closed center type, usually effect acompensation at the pump or at the valve. ln order to handle a pluralityof functions, there is usually employed a tandem or priority type valvecircuit for establishing the necessary control of flow. Such systemshave been somewhat successful in providing efficient control to anyfunction since they have the characteristic of supplying a set flow(variable by positioning of the valve) to the function regardless of thepressure requirement. While such systems have achieved a modicum ofsuccess. their disadvantage is that they have usually employed a fixeddisplacement pump such that the pump must supply full flow at whateveris required by the highest pressure function being performed.

Another system known to the art, and of more recent origin. incorporatesa pressure-compensated pump attached to a modified parallel circuitvalve. In this circuit the pump is controlled both in pressure and inflow; thereby exhibiting considerable horse power savings over thepreviously described systems. The primary disadvantage inherent withinsuch a system is caused by the fact that only one function. that havingLII the highest pressure. is flow-compensated. Thus. only that portionof the circuit has the precise control desired.

Another more recent. and somewhatsuccessful attempt to meet this need inthe art has been to provide a compensator system which generallycomprises a variable delivery pump. the output of which is controlled bya signal delivered from a modified open centered control valve. Thesystem includes a control cylinder having a piston for operating acontrol cam of the variable delivery pump. first and second feedbackcircuits provided to govern operation of the control cylinder. the firstfeedback cylinder including an open center position of the control valveand the second feedback circuit including a circuit through a pressuredifferential valve. Such a system can provide a series of controlvalves. each of which can be compensated. While such a system is quiteadvantageous. it has the disadvantage that compensation can only beapplied on one valve at a time and thus there is not provided. a fullycompensated system.

It is evident from the above that there exists a need in the art for asystem which can provide compensation of all functions regardless of thefact that the functions have different requirements. It is alsoapparent. that there exists a need in the art for such a compensatingsystem. which includes many of the advantages of the above-describedprior art. particularly with respect to the advantages achieved by usingpressure compensated valve components. but which either mitigates oreliminates the disadvantages attendant therewith.

SUMMARY OF THE INVENTION It is a purpose of this invention to fulfillthe abovedescribed needs in the art. and other needs which will becomemore apparent to the skilled artisan once given the followingdisclosure.

In general. the unique systems of this invention comprise hydraulicsystems capable of adjusting the output ofa variable delivery pump inresponse to the varying demands of any one of at least two hydraulicallyoperated functions. the system comprising at least two control valvemeans each capable of performing a separate function. each of said valvemeans being connected to its own compensator valve means. saidcompensator valve means being connected in series one with the other andbeing capable of delivering the necessary amount of hydraulicfluid toits respective control valve means in accordance with the full needsthereof and diverting the remainder of the fluid to the next followingcompensator valve means. and means connected to the compensator valvemeans farthest from said pump for sensing the total requirement of thesystem and for adjusting the output of the pump in response thereto.

In certain preferred embodiments. the means for sensing and adjustingthe output of the pump includes a restricted orifice means. a controlvalve. and means for sensing the pressure drop across said restrictedorifice means, said control valve being connected through a port to anadjustor means for adjusting the output of said pump and being normallybiased by said means for sensing said pressure drop so as to actuatesaid adjustor means in favor of providing a minimal continuous flow offluid through said system regardless of the total requirements of thesystem. I

This invention will now be described with more particularity and withreference to' arious illustrations wherein:

lN THE DRAWINGS The accompanying FIGURE is a schematic illustration of aparticularly preferred embodiment of this invention.

DETAILED DESCRIPTION OF THE lNVENTlON Referring to the FIGURE there ispresented a system for controlling a plurality (in this instance. two)of functions simultaneously. economically. with low heat loss andexcellent control. despite the use of only a single pump means. In thisFIGURE. there is illustrated a pump 1 preferably of the variabledelivery (i.e.. variable volume) type. The delivery of pump 1 isvariable by spring biased lever 3 which is actuated against its biasingspring 5 by movement of piston 7 located in cylinder 9. Pump 1 isprovided with a tank outlet line 11 and a fluid output line 13. Line 11leads from tank. represented as T. while line 13 leads to the workfunction areas designated as A and B.

While this FIGURE illustrates the compensation of only two work functionareas A and B. it is understood that more than two areas could becompensated for merely by providing such areas between A and B and inlike series therewith. The limitation on the number of work functionareas is governed primarily by way of the practical limits placed uponpump 1 in that the pump 1 must provide the total requirements of all ofthe functions being performed.

In the embodiment shown, function areas A and B may perform separate anddistinct functions such as for example. function area A lifting a boomwhile function area B moves a bucket. In this embodiment. then. functionarea A is provided with a conventional closed center control valve 15, aconventional pressure compensator valve 17 and a conventional shuttlevalve 19. Work function area B is provided with similar components andthey have been similarly numbered with the corresponding primedreference characters.

Compensator valve 17 is connected in series with valve 17' via line 21.Each of the compensator valves 17 and 17 is connected to its respectivecontrol valve 15 and 15 via lines 23 and 23' respectively. In addition.the compensator valves 17 and 17 are biased to their correct positionfor flow or nonflow by way of movement of control spools and 25'.respectively (as by an operator), via conventional shuttle valves 19 and19'. respectively.

While line 21 is connected in series with compensator valve 17' (that isto say. each work function area A except for the last work functionarea. will have its line 21 connected to the next following pressurecompensator valve), the last line 27 of the last compensator valve 17'leads to a means for sensing the total requirements of the system. andadjusting the output flow of pump in response thereto. Such a sensingand adjusting means includes a restrictive orifice 29 and a controlvalve generally illustrated at 31. Such a control valve 31 generallycomprises a variable spool 33 biased to the right by spring 35, pilotsignal ports 37 and 39. tank port 41, control port 43 and pressure port45. Pilot signal port 39 allows fluid to bias spool 33 to the leftagainst the action of its biasing spring in an amountdepending upon theflow sensed via line 47 at the upstream end of restricted orifice 29.Similarly. spool 33 is biased in the direction of its spring 35 viasignal from line 49 which senses the flow at the downstream end ofrestricted orifice 29.

Pressure port receives pressure from pump via line 55. Control port 43is connected to cylinder 9 via line 53 while tank port 41 is connectedto tank T via line 49. Valve 57 represents a conventional relief valveto limit maximum pressure. Line 51' extends from control valve 15' totank T.

The unique compensating features of this invention will now be morefully understood by reference to a typical operation of this system whenput into use. Assume that initially. the system has no load imposed uponit and that it is desired to idle the system with a minimum amount ofeffort and power input. This is accomplished. for most systemscontemplated by this invention. by allowing pump 1 to pump a sufficientamount of hydraulic fluid through the system such that the pressure dropacross the system (i.e.. for this system. through the compensator spoolsection of the valves) is maintained at whatever minimum pressure isrequired for control only. In most preferred circuits this may beaccomplished by providing a 1-2 gallon per minute flow through orifice29. Thus. by taking any given individual system and. throughconventional engineering techniques coordinating size of orifice 29 withthe bias of spring 35, a system will be provided to establish just sucha flow. This may be accomplished as follows:

After orifice 29 and spring 35 are installed. pump 1 is turned on atsome low value so as to establish flow in the system usually at a levelabove that minimal flow ultimately desired. Since no work function isbeing performed by either area A or area Bfflow from pump 1 extends vialine 13 through line 21 and outwardly to sensing means via line 27. Thepressure upstream of restricted oriflce 29 is sensed by line 47 andtransmitted to pilot signal port 39 where it biases spool 33 againstspring 35. The pressure drop across orifice 29 is then sensed via line49 and transmitted to pilot signal port 37 which compensates. to theextent of the pressure drop, the biasing caused by the higher pressurein port 39. This bias causes spool 33 to be adjusted such that therequisite amount of pressure is transmitted via line 53 and intocylinder port 9 to actuate movement of piston 7 against the bias ofspring 5 thus to adjust pump 1 so that. at idle. line 13 transmitssufficient fluid to maintain a minimal flow through and acrossrestricted orifice 29. As stated hereinabove. a typical example of suchminimal flow is about l-2 gallons per minute across orifice 29 with apressure drop of about psi.

With the system now in its idle condition. an operator may wish tooperate a function such as raise the main boom of an excavator. He maydo so by actuating control spool handle 25 to the degree necessary toperform the function. This shift of spool 25 effects the necessary shiftin valve 15 such that a signal is sent via shuttle valve 19 and line 59to shift pressure compensator valve 17 so as to supply control valve 15with the necessary amount of fluid to perform its function through itswork ports. Thus. pressure compensator valve 17 provides all of the flownecessary to perform the function in work area A and diverts (ifavailable) the remainder of the fluid via line 21 to pressurecompensator valve 17'. In the event. of course. that there isinsufficient fluid to perform the function in work area A. then. of

course, the sensing means will sense this lack. and increase the outputof pump 1 via line 13 suchthat the necessary amount of flow .is created.to :perform the work function and in addition to provide for thepressure drop across orifice 29 of the system in like manner as whenidle.

Now with the excess fluid diverted via line 21 to pressure compensatorvalve 17'. the function of work area B may beperformed by activatingspool When this is done. pilot line 59' signals, via shuttle valve 19',pressure compensator valve 17' to provide the necessary flow via line23' to the work ports of control valve 15' to perform the necessaryfunction. The excess (if present) passes via line 27 across orifice 29and this differential pressure is again sensed via lines 49 and 47similarly as with respect to work function area A above so as tocompensate the output of pump 1 thereby providing for the necessary flownot only for work area A but work area B as well. A similar type ofcompensation. of

course, also takes place should there not be any flow left or shouldthere be insufficient flow to perform the work function in area B. In asimilar manner, further additional work areas may be added between areaA and area B to perform further functions and be similarly compensated.

As can be seen, the unique systems of this invention adopt many of theexcellent features of pressure com pensated valve components in thatextremely good control to any single function is provided becausepressure is maintained and determined by the highest load requirementwhile flow is compensated for in a uniquely efficient manner. On theother hand, the detriments of using only conventional noncompensatedvalves and of only compensating the highest requirement with the pumphave been overcome. Thus. the subject invention has provided, through aunique system, a circuit which individually controls flow at each portor function and combines this with the ability to signal the pump tosupply only that amount of flow required to satisfy any and every givenfunction. In addition, any singular valve spool has the ability tosupply full flow to its function, but, if a preceding spool is shiftedto some intermediate position, then that spool has priority to someportion of the flow. Such a system,

by building in this unique and small constant flow requirement, providesfor a system which results in an extremely low horse power loss and lowheat generation factor which, of course, provides for an extremelyefficient and economical system.

Once given the above disclosure, various other features, modificationsand improvements will become apparent to the skilled artisan. Such otherfeatures, modifications and improvements, therefore, are considered tobe a part of this invention, the scope of which is to be determined bythe following claims:

I claim:

1. A hydraulic system capable of adjusting the output of a variabledelivery pump in response to the varying demands of any one of at leasttwo hydraulically operated functions, the system comprising at least twocontrol valve means each capable of performing a separate function, atleast two of said control valve means each being connected to its ownupstream compensator valve means, said compensator valve means beingconnected in series one' with the other and each being capable ofdeliverying the necessary amount of hydraulic fluid to its respectivecontrol valve means in accordance with the full needs thereof anddiverting the remainderof said fluid to the next following compensatorvalve means. and means connected to said compensator valve meansfarthest from said pump-for sensing the total requirement of the systemdespite the varying demands of said functions and for adjusting theoutput of the pump in response thereto.

1 LA hydraulic system according to claim 1 in which the pressure of thesystem is determined by the highest load requirement of a function andadjustment is achieved by varying the flow rate of said pump.

3. A hydraulic system capable of adjusting the output of a variabledelivery pump in response to the varying demands of any one of at leasttwo hydraulically operated functions, the system comprising at least twocontrol valve means each capable of performing a separate function, eachof said control valve means being connected to its own compensator valvemeans, said compensator valve means being connected in series one withthe other and each being capable of delivering the necessary amount ofhydraulic fluid to its respective control valve means in accordance withthe full needs thereof and diverting the remainder of said fluid to thenext following compensator valve means, and means connected to saidcompensator valve means farthest from said pump for sensing the totalrequirement of the system despite the varying demands of said functionsand for adjusting the output of the pump in response thereto, said meansfor sensing and adjusting includes a restricted orifice means, a controlvalve. and means for sensing the pressure drop across said orificemeans. said control valve being connected through a port to an adjustormeans for adjusting the output of said pump. and being normally biasedby said means for sensing said pressure drop so as to actuate saidadjustor means in favor of providing a minimal continuous flow of fluidthrough the system regardless of the total requirement of the system.

4. A hydraulic system according to claim 3 wherein said means forsensing the pressure drop across said orifice means includes two flowlines, one on either side of said orifice, and said control valveincludes a control valve spool and abiasing spring, and wherein the flowline upstream of said orifice is connected to bias said spool againstits biasing spring and said flow line downstream of said orifice isconnected to bias said spool with said spring. I

5. A hydraulic system according to claim 4 wherein said adjustor meansincludes a cylinder connected through said port to said control valve, apiston located in said cylinder and being biased against fluid flow fromsaid port by a spring, and a lever arm means actuated by movement ofsaid cylinder for increasing or decreasing the output of said pump.

6. A hydraulic system according to claim 5 wherein said control valvemeans include control valves each of which is connected to a separateshuttle.

7. A hydraulic system according to claim 6 wherein each control valve isconnected to its compensator valve means and shuttle valve such thatwhen said control valve is actuated to perform a function, said shuttlevalve senses the fluid requirement to perform said function andactivates said compensator valves means to fulfill said requirement infull and to divert excess fluid to said next compensator valve means insaid series.

8. A hydraulic system according to claim 7 in which the pressure of thesystem is determined by the highest 8 said pressure drop so as toactuate said adjustor means in favor of providing a minimal continuousflow of fluid through the system regardless of the total requirement ofthe system.

10. A hydraulic system according to claim 9, wherein said compensatorvalve means are located upstream from each of their associated controlvalve means.

1. A hydraulic system capable of adjusting the output of a variabledelivery pump in response to the varying demands of any one of at leasttwo hydraulically operated functions, the system comprising at least twocontrol valve means each capable of performing a separate function, atleast two of said control valve means each being connected to its ownupstream compensator valve means, said compensator valve means beingconnected in series one with the other and each being capable ofdeliverying the necessary amount of hydraulic fluid to its respectivecontrol valve means in accordance with the full needs thereof anddiverting the remainder of said fluid to the next following compensatorvalve means, and means connected to said compensator valve meansfarthest from said pump for sensing the total requirement of the systemdespite the varying demands of said functions and for adjusting theoutput of the pump in response thereto.
 1. A hydraulic system capable ofadjusting the output of a variable delivery pump in response to thevarying demands of any one of at least two hydraulically operatedfunctions, the system comprising at least two control valve means eachcapable of performing a separate function, at least two of said controlvalve means each being connected to its own upstream compensator valvemeans, said compensator valve means being connected in series one withthe other and each being capable of deliverying the necessary amount ofhydraulic fluid to its respective control valve means in accordance withthe full needs thereof and diverting the remainder of said fluid to thenext following compensator valve means, and means connected to saidcompensator valve means farthest from said pump for sensing the totalrequirement of the system despite the varying demands of said functionsand for adjusting the output of the pump in response thereto.
 2. Ahydraulic system according to claim 1 in which the pressure of thesystem is determined by the highest load requirement of a function andadjustment is achieved by varying the flow rate of said pump.
 3. Ahydraulic system capable of adjusting the output of a variable deliverypump in response to the varying demands of any one of at least twohydraulically operated functions, the system comprising at least twocontrol valve means each capable of performing a separate function, eachof said control valve means being connected to its own compensator valvemeans, said compensator valve means being connected in series one withthe other and each beinG capable of delivering the necessary amount ofhydraulic fluid to its respective control valve means in accordance withthe full needs thereof and diverting the remainder of said fluid to thenext following compensator valve means, and means connected to saidcompensator valve means farthest from said pump for sensing the totalrequirement of the system despite the varying demands of said functionsand for adjusting the output of the pump in response thereto, said meansfor sensing and adjusting includes a restricted orifice means, a controlvalve, and means for sensing the pressure drop across said orificemeans, said control valve being connected through a port to an adjustormeans for adjusting the output of said pump, and being normally biasedby said means for sensing said pressure drop so as to actuate saidadjustor means in favor of providing a minimal continuous flow of fluidthrough the system regardless of the total requirement of the system. 4.A hydraulic system according to claim 3 wherein said means for sensingthe pressure drop across said orifice means includes two flow lines, oneon either side of said orifice, and said control valve includes acontrol valve spool and a biasing spring, and wherein the flow lineupstream of said orifice is connected to bias said spool against itsbiasing spring and said flow line downstream of said orifice isconnected to bias said spool with said spring.
 5. A hydraulic systemaccording to claim 4 wherein said adjustor means includes a cylinderconnected through said port to said control valve, a piston located insaid cylinder and being biased against fluid flow from said port by aspring, and a lever arm means actuated by movement of said cylinder forincreasing or decreasing the output of said pump.
 6. A hydraulic systemaccording to claim 5 wherein said control valve means include controlvalves each of which is connected to a separate shuttle.
 7. A hydraulicsystem according to claim 6 wherein each control valve is connected toits compensator valve means and shuttle valve such that when saidcontrol valve is actuated to perform a function, said shuttle valvesenses the fluid requirement to perform said function and activates saidcompensator valves means to fulfill said requirement in full and todivert excess fluid to said next compensator valve means in said series.8. A hydraulic system according to claim 7 in which the pressure of thesystem is determined by the highest load requirement of a function, andadjustment is achieved by varying the flow rate of said pump.
 9. Ahydraulic system according to claim 8 wherein said means for sensing andadjusting includes a restricted orifice means, a control valve, andmeans for sensing the pressure drop across said orifice means, saidcontrol valve being connected through a port to an adjustor means foradjusting the output of said pump, and being normally biased by saidmeans for sensing said pressure drop so as to actuate said adjustormeans in favor of providing a minimal continuous flow of fluid throughthe system regardless of the total requirement of the system.